Panel structure and pallet utilizing same

ABSTRACT

A twin sheet plastic panel structure, a twin sheet plastic pallet utilizing the panel structure, and a methodology for forming the panel structure and pallet. The panel structure is formed by thermoforming an upper plastic sheet to include rows of hollow bosses extending downwardly from the main body of the sheet; thermoforming a lower plastic sheet to include rows of hollow bosses extending upwardly from the main body portion of the sheet; and bringing the sheets together while still in a heated flowable state to position the bosses of the upper sheet in intermeshing relation to the bosses of the lower sheet so that the annular side wall portions of the upper and lower bosses fuse together, the bottom walls of the upper sheet bosses are fused to the upper surface of the main body portion of the lower sheet, and the upper walls of the lower sheet bosses are fused to the lower surface of the main body portion of the upper sheet to form a series of parallel rigid column structures between the sheets. In the case of the pallet, the fused together upper and lower sheets coact to define a platform structure for the pallet and the upper and lower sheets further coact to define a plurality of legs extending downwardly from the platform structure to position the platform structure in spaced relation to a support surface.

RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.07/993,762, filed Dec. 18, 1992.

BACKGROUND OF THE INVENTION

This invention relates to panel structures and to plastic palletsembodying panel structures according to the invention.

Panel structures are in wide use for construction purposes andfabricating purposes. Prior art panel structures have been formed ofeither metal, a paper product such as cardboard, wood, or syntheticmaterials such as plastic. Panel structures ideally are lightweight,strong, durable and maintenance-free, provide all-weather performance,and are relatively inexpensive. Whereas a plurality of metal, paper,wood, and plastic panel structures have been proposed over the years,none have totally satisfied all of the above-noted criteria.

Panel structures are also widely used in packaging and, specifically, inthe formation of pallets. Pallets have traditionally been formed ofwood. Wood pallets, however, have many disadvantages. For example, theyare subject to breakage and thus are not reusable over extended periodsof time. Wood pallets also take up a considerable amount of valuablefloor space in the warehouse when they are not in use. In an effort tosolve some of the problems associated with wood pallets, plastic palletshave been developed and employed with some degree of success. In onegenerally successful form of plastic pallet design, upper and lowerplastic sheets are formed in separate molding operations and the twosheets are then selectively fused or knitted together in a suitablepress to form a reinforced double wall or "twin sheet" structure. Thesetwin sheet plastic pallets, although substantially more durable than thewooden pallets that they replace, tend to have a substantially higherinitial cost than the corresponding wooden pallets due in large part tothe relatively high cost of the raw plastic material required to formthe pallet. It is therefore critical that the twin sheet type of palletembody a structural design that maximizes the structural strength of thepallet for a given amount of plastic material employed to form thepallet. One form of twin sheet type plastic pallet that provides highstructural strength for a given amount of plastic material is shown inapplicant's U.S. Pat. No. 4,879,956. However, even the improved designof this patent is unable to provide the necessary rigidity required formany pallet applications without utilizing increased amounts of plasticmaterial and thereby adding to the expense of the pallet.

SUMMARY OF THE INVENTION

This invention is directed to the provision of an improved panelstructure that is lightweight, strong, durable, provides all-weatherperformance, and is relatively inexpensive.

This invention is more specifically directed to the provision of animproved plastic pallet that provides extremely high structural strengthfor a given amount of plastic material employed to form the pallet.

The twin sheet panel structure of the invention comprises a firstplastic sheet including a planar main body portion having inner andouter surfaces and a second plastic sheet positioned in parallel spacedrelation to the first plastic sheet and including a main body portionhaving inner and outer surfaces. The first sheet further includes aplurality of spaced hollow bosses opening in the outer surface of thefirst sheet main body portion and including annular side wall portionsextending inwardly from the first sheet main body portion andterminating in inner wall portions fused in spaced relation to the innersurface of the main body portion of the second sheet, and the secondsheet further includes a plurality of spaced hollow bosses opening inthe outer surface of the second sheet main body portion and includingannular wall portions extending inwardly from the second sheet main bodyportion and terminating in inner wall portions fused in spaced relationto the inner surface of the first sheet main body portion.

According to an important feature of the invention, the annular sidewall portions of some of the first sheet bosses are fused to the annularside wall portions of some of the second sheet bosses. The fusedtogether annular side wall portions of the first and second sheets coactto provide an extremely rigid panel structure for a given amount ofplastic material.

According to a further feature of the invention, the first sheet bossesare arranged in rows with the bosses in each row laterally spaced fromeach other and the second sheet bosses fit into the spaces between thefirst sheet bosses. The positioning of the first sheet bosses betweenthe second sheet bosses, with the first sheet bosses fused to the secondsheet and the second sheet bosses fused to the first sheet, provides anextremely rigid panel structure for a given amount of plastic material.

According to a further feature of the invention, the bosses are arrangedon each sheet in a plurality of generally parallel laterally extendingrows with the bosses in each row spaced laterally from each other, andthe bosses in a row of the first sheet are interdigitated with respectto the bosses in a corresponding row of the second sheet with theadjacent side wall portions of the interdigitated bosses fused together.This arrangement has the effect of forming a plurality of rigid columnstructures between the sheets corresponding to the rows and produces anextremely rigid panel structure for a given amount of plastic material.

In the invention plastic pallet, the pallet comprises a twin sheetplatform structure formed in accordance with the above-noted features ofthe invention panel structure and the pallet further includes aplurality of spaced legs extending downwardly from the platformstructure to position the platform structure in upwardly spaced relationto a support surface on which the legs are positioned.

Also disclosed is a further form of a plastic pallet formed inaccordance with the above-noted features of the invention panelstructure but embodying a double faced configuration including an upperpanel structure according to the invention defining a platform sectionfor the pallet and a lower panel structure according to the inventiondefining a flat base on which the pallet may rest.

The invention also provides a methodology for forming an improved panelstructure as well as a methodology for forming an improved palletstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a panel structure according to theinvention;

FIGS. 2 and 3 are cross-sectional views taken respectively on lines 2--2and 3--3 of FIG. 1;

FIG. 4 is a fragmentary view looking in a direction of the arrow 4 inFIG. 1;

FIG. 5 is a fragmentary view showing steps in the methodology of thepresent invention;

FIG. 6 is a fragmentary view on an enlarged scale looking in thedirection of the arrow 6 in FIG. 1

FIG. 7 is a fragmentary plan view of the invention panel structure;

FIG. 8 is cross-sectional view taken on lines 8--8 of FIG. 6;

FIG. 9 is an exploded view of the invention panel structure;

FIG. 10 is a perspective view of a pallet according to the invention;

FIGS. 11 and 12 are cross-sectional views taken respectively on lines11--11 and 12--12 of FIG. 10;

FIG. 13 is a perspective view of a double faced pallet according to theinvention;

FIG. 14 is a fragmentary side view of the pallet of FIG. 13;

FIG. 15 is a cross-sectional view taken on line 5--15 of FIG. 15;

FIG. 16 is a perspective view of another double faced pallet accordingto the invention;

FIG. 17 is a fragmentary side view of the pallet of FIG. 16;

FIG. 18 is a cross-sectional view taken on line 18--18 of FIG. 16; and

FIGURE 19 is a fragmentary top view of the pallet of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In broad overview, the panel structure 10 seen in FIGS. 1-9 and thepallet seen in FIGS. 10-12 are both preferably formed in a vacuumforming process preferably embodying a plastic twin sheet constructionemploying two polyethylene sheets or skins which are selectivelythermoformed and are then fused or knitted together at various points,while still in a heated state, to form the panel structure or thepallet.

Panel structure 10 is formed from a thermoformed, selectively configuredupper sheet 14 and a thermoformed, selectively configured lower sheet16. In the disclosed panel structure, each sheet 14 and 16 has agenerally rectangular configuration but the configuration of the sheetswill of course vary depending upon the desired configuration of thefinal panel structure.

Sheet 14 is formed in known manner in coaction with an upper vacuumforming mold 18 and sheet 16 is formed in known manner in coaction witha lower vacuum forming mold 20. Specifically, sheet 14 is heated,positioned in underlying relation to the mold 18, and then suckedupwardly into conformance with the surface 18a of the mold 18 utilizingvacuum ports 18b. Similarly, sheet 16 is heated, positioned in overlyingrelation to mold 20, and sucked downwardly into conformance with thesurface 20a of mold 20 utilizing vacuum ports 20b. After the sheets havebeen thus thermoformed, and with the sheets still in a heated flowablestate, the molds 18 and 20 are moved together to selectively fuse theupper sheet to the lower sheet.

Molds 18 and 20 are configured such that, following the thermoformingoperation, each sheet includes a generally planar main body portion anda plurality of spaced hollow bosses extending from the planar main bodyportion.

Specifically, upper sheet 14 is thermoformed to include a generallyplanar main body portion 14a and a plurality of spaced hollow bosses 14bopening in the upper or outer surface 14c of the main body portion andincluding downwardly tapering conical annular side wall portions 14d ofgenerally circular cross-sectional configuration extending downwardlyfrom the main body portion and terminating in inner or bottom circularwall portions 14e. Bosses 14b are arranged in rows 14f with each rowstaggered with respect to the next adjacent row so that the bosses inone row are positioned generally between adjacent bosses in adjacentrows.

Similarly, lower sheet 16 is thermoformed to include a main body portion16a and a plurality of spaced hollow bosses 16b opening in the lower orouter surface 16c of the main body portion and including upwardlytapering conical annular wall portions 16d of generally circularcross-sectional configuration extending upwardly from the main bodyportion 16a and terminating in upper or inner circular wall portions16e. Bosses 16b are arranged in rows 16f with each row staggered withrespect to the next adjacent row so that a boss in one row is positionedbetween adjacent bosses in an adjacent row.

Rows 16f are also staggered with respect to the corresponding rows 14fin the upper sheet so that when the sheets 14 and 16 are fitted togetherto form the panel structure, each boss 14b of upper sheet 14 fitsinterdigitally between a pair of adjacent bosses 16b of the lower sheetand each boss 16b of the lower sheet fits interdigitally between a pairof adjacent bosses 14b of the upper sheet. The downward angle or taperof the bosses 14b is complementary to the upward angle or taper of thebosses 16b so that when the bosses are fitted or meshed together, and asbest seen in FIG. 2, the bosses fit together along angular interfaces22.

Since the sheets are fitted together while still in a heated, flowablestate, the bosses are fused together along their angled interfaces 22.Further, since the bosses 14b and 16b have equal vertical extents orheights, the respective walls 14e and 16e of the bosses are fused to therespective confronting faces of the main body portions of the respectivesheets. Specifically, the lower or inner wall 14e of an upper sheet boss14b is fused to the upper surface 16g of lower sheet main body portion16a at a location between a respective pair of lower sheet bosses 16b,and the upper or inner wall 16e of a lower sheet boss 16b is fused tothe lower or inner surface 14g of upper sheet main body portion 14abetween a respective pair of upper sheet bosses 14b.

As best seen in FIG. 5, the sheets are configured such that bosses 14band 16b have identical configuration and further such that the dimensionA measured across the valley or root of the upper mold 18 betweenadjacent mold boss configurations 18c is identical to the dimension Bmeasured across the top of the boss configuration 20c of the lower mold.This configuring of the upper and lower molds provides an interferenceor overlapping fit as between the upper and lower bosses as the sheetsare pressed together so that the upper and lower bosses, rather thanmerely fusing along a line of angular contact, fuse along a relativelywide area of contact as seen by the dashed lines 24 in FIG. 8. As bestseen in FIG. 8, the fused together bosses coact to form a plurality ofrigid column structures 26 between the upper and lower sheetscorresponding in arrangement and orientation to the boss rows 14f and16f of the upper and lower sheets. As best seen in FIG. 4, spaces oropenings 28, running the entire width of the panel structure, are formedbetween rigid column structures 26.

Whereas the dimensions of the individual bosses, the spacing betweensuccessive bosses in each row, and the spacing between rows will varydepending upon the particular application for which the panel structureis intended, certain dimensional relationships as between the bossconfigurations, boss spacings, and row spacings have been found to beparticularly advantageous in terms of producing an extremely strongpanel structure for a given amount of plastic material. Specifically,and as best seen in FIGS. 6 and 7, a particularly strong panel structureis provided by relating the boss and other dimensions to the overallthickness X of the panel structure such that the major dimension of eachboss (i.e., the dimension of the boss as it opens in the associated mainbody structure) is equal to X; the minor dimension on of each boss(i.e., the dimension of the boss at its inner wall) is equal to one halfX; the distance centerline to centerline between successive bosses ineach row is equal to 1.5X; and the distance centerline to centerlinebetween adjacent rows is equal to 1.5X. This specific dimensionalinterrelationship produces a rigid panel structure in which the combinedarea of the openings of the downwardly extending bosses of the uppersheet in the upper surface of the upper sheet main body portionconstitutes approximately 35% of the total surface area of the uppersurface of the main body portion of the upper sheet and the combinedarea of the openings of the upwardly extending bosses of the lower sheetin the lower surface of the lower sheet main body portion constitutesapproximately 35% of the total surface area of the lower surface of themain body portion of the lower sheet. This specific dimensionalinterrelationship has further been found to allow the sheets to drawsmoothly, and without excessive thinning, over the respective molds toprovide a final panel structure that is extremely strong and rigid incomparison to the amount of plastic material utilized.

The pallet 12 seen in FIGS. 10-12 utilizes a panel structurecorresponding to the panel structure 10, and is formed in a mannergenerally similar to the formation of panel structure 10, except thatthe upper and lower sheets of the twin sheet pallet are furtherselectively thermoformed to provide spaced legs extending downwardlyfrom the main body or platform structure of the pallet to position theplatform structure in upwardly spaced relation to a support surface onwhich the legs are positioned.

Specifically, pallet 12 includes upper and lower plastic sheets 30 and32; upper sheet 30 includes a main body portion 30a and a plurality ofspaced hollow bosses 30b opening in the upper surface 30c of the mainbody portion and including tapered conical annular side wall portions30d extending downwardly from the upper sheet main body portion andterminating in inner or bottom circular wall portions 30e; lower sheet32 includes a main body portion 32a and a plurality of spaced hollowbosses 32b opening in the lower surface 32c of the main body portion andincluding tapered conical annular side wall portions 32d extendingupwardly from the lower sheet main body portion and terminating in upperor inner circular wall portions 32e; the bosses in the upper sheet arearranged in rows 30f with each row staggered with respect to the nextadjacent row so that a boss in one row is positioned between adjacentbosses in the next adjacent row; the bosses in the lower sheet arearranged in rows 32f that are staggered with respect to each adjacentrow in the lower sheet and are also staggered with respect to thecorresponding rows in the upper sheet so that the upper and lower bossesfit together in intermeshing fashion in the manner described withrespect to the panel structure 10; the intermeshed and fused togetherupper and lower sheets coact to define a platform structure 34 of thepallet including rigid column structures 40 extending across theplatform structure; and the upper and lower sheets are furtherselectively thermoformed to define downwardly extending leg portions 30fand 32f which are fused together in nesting relationship as the sheetsare brought together to define a plurality of spaced legs 36 extendingdownwardly from platform structure 34 to position the platform structurein upwardly spaced relation to a support surface on which the pallet ispositioned. For example, for a nine-legged pallet, the upper and lowersheets are configured to define four corner legs 36, a further leg 36along each side edge of the pallet between corner legs, and a centralleg positioned at the proximate midpoint of the pallet. The upper andlower sheets may be further configured to define edge portions 30g and32g which are fused together as the sheets are brought together to forma peripheral bead 38 extending around the periphery of the pallet andsealing off the interior of the platform section 34.

As with the panel structure, the relative dimensions of the bosses, thespacing between bosses in a given row, and the spacing between adjacentrows may vary depending upon the particular application for which thepallet is intended but, also as with the panel structure 10, aparticularly strong pallet structure for a given amount of plasticmaterial has been found to result from a pallet in which the variousparameters are related to the thickness X of the platform structure 34such that each boss has a major dimension equal to X and a minordimension equal to one half X; the distance between centerlines ofsuccessive bosses in each row is equal to 1.5X; and the distance betweencenterlines of adjacent rows is equal to 1.5X. As previously noted withrespect to panel structure 10, these specific parameters and dimensionalinterrelationship produce a rigid panel structure in which the combinedarea of the openings of the downwardly extending bosses of the uppersheet in the upper surface of the upper sheet main body portionconstitutes approximately 35% of the total surface area of the uppersurface of the main body portion of the upper sheet and the combinedarea of the openings of the upwardly extending bosses of the lower sheetin the lower surface of the lower sheet main body portion constitutesapproximately 35% of the total surface area of the lower surface of themain body portion of the lower sheet. As also previously noted withrespect to panel structure 10, these specific parameters have been foundto provide a smooth draw or flow behavior of the plastic sheets as theplastic material is drawn over the bosses of the molds with minimumthinning of the plastic material even in the deep draw sections, and hasbeen found to produce an extremely rigid pallet for a given amount ofplastic material employed to form the pallet.

The double faced pallet 50 seen in FIGS. 13-15 utilizes a panelstructure according to the invention to form the upper or platformsection of the pallet and a further panel structure according to theinvention to form a flat lower base portion for the pallet on which thepallet may rest, and is further configured to define pillar structuresinterconnecting the upper and lower panel structures and also embodyingthe constructional features of the panel structure of the invention.

Specifically, the double faced pallet 50 in FIGS. 13-15 includes anupper panel structure 52 corresponding to the panel structure 10 of FIG.1, a lower panel structure 54 corresponding to the panel 10 of FIG. 1but having a lesser thickness than the panel structure 52, and aplurality of pillar structures 56 (for example nine, including fourcorner pillar structures, a pillar structure intermediate each pair ofcorner pillar structures, and a central pillar structure)interconnecting the upper and lower panel structures and coacting todefine forklift entry passages 58 to allow entry of a forklift truckfrom any side of the pallet.

Each pillar structure 56 is also formed utilizing panel structuresaccording to the invention. Specifically, each pillar structure 56includes stacked upper and lower panel structures 59 and 60 with eachupper and lower panel structure corresponding to the construction of thepanel of FIG. 1 but having reduced dimensions as compared to the upperand lower panel structures 52 and 54 so as to provide the prescribednine spaced pillar structures defining forklift corridors 58therebetween. As shown, the panel structures 59 and 60 constituting eachpillar 56 may have a thickness corresponding to the upper panelstructure 52 and the lower panel structure 54 may have a thicknessapproximately κ the thickness of the panel structures 52, 59 and 60.

The main body portion 62a of tile lower sheet 62 of the upper panelstructure 52 is fused to the main body portion 64a of the upper sheet 64of the panel structure 59; the main body portion 66a of the lower sheet66 of panel structure 59 is fused to the main body portion 68a of theupper sheet 68 of the panel structure 60; and the main body portion 70aof the lower sheet 70 of the panel structure 60 is fused to the mainbody portion 72a of the upper sheet 72 of the panel structure 54 so thateach set of intermediate panel structures 59 and 60 coact with selectedportions of the upper and lower panel structures 52 and 54 to form arigid column interconnecting the upper and lower panel structures and sothat the panel structures 56 in combination coact to rigidlyinterconnect the upper and lower panel structures at nine spacedlocations corresponding to the usual leg locations in a standardnine-legged pallet. In the finished pallet, lower panel structure 54defines a base structure on which the pallet may rest, upper panelstructure 52 defines a platform structure defining an upwardly facingload receiving surface 74, and the pallet may be selectively movedutilizing forklifts positioned in tile passages 58.

The pallet 76 shown in FIGS. 16-19 is also a double faced palletutilizing the panel structure of the invention. Specifically, the pallet76 of FIGS. 16-19 is formed of a twin sheet upper deck structure 78 anda twin sheet lower deck structure or base 80. Deck structures 78 and 80are identical and the pallet is formed by inverting lower deck structure80 relative to upper deck structure 78 and fusing the decks together attheir interfaces to form forklift passageways 82. Deck 78 is formed ofupper and lower thermoformed plastic sheets 84 and 86. Sheets 84 and 86are formed over the majority of their surface areas (with the exceptionof the areas corresponding to the legs or columns of the pallet) in amanner to duplicate the structure of the panel of Figure I with theupper and lower sheets providing downwardly extending and upwardlyextending intermeshing bosses to provide rigid columns extending thewidth of the pallet in the manner described with respect to the panelstructure of FIG. 1. As best seen in FIG. 19, the columns formed by theintermeshing upwardly and downwardly extending bosses on the upper andlower sheets may be arranged to run from left to right of the pallet asviewed in FIG. 16 except for border portions along the left and rightborders of the pallet as viewed in FIG. 16 where the columns may bearranged to run from bottom to top of the pallet.

The upper and lower sheets 84 and 86 also provide downwardly andupwardly extending intermeshing bosses in the regions corresponding tothe legs or columns of the pallet but the bosses in these regions aremuch larger than the bosses in the main deck region of the upper decksection 76. Specifically, upper sheet 84 is configured in each legregion to provide a plurality of large downwardly extending upwardlyopening bosses 84a having side walls meshingly coacting with and fusedto the side walls of large upwardly extending downwardly opening bosses86a of the lower sheet 86. As best seen in FIG. 19, the intermeshing,fused together bosses in each leg or column section of the pallet arearranged in a rectangular configuration so that the upwardly anddownwardly extending bosses coact to form a rectangular wall or columnrepresented by the dash line 88 in FIG. 19 with further bosses providedwithin the wall 88 to provide a linear column or wall 98 encircled bythe rectangular column or wall 88. The wall 88 is solid along its outerperipheral sides 88a and 88b but, as best seen in FIG. 18, definesopenings 92 between the bosses along the inner wall portion 88c and 88d.Openings 92 do not extend completely through the wall portion 88c and88d but rather simply open up in the interior of the associated upwardlyextending boss 86a.

As indicated, lower deck 80 is identical to upper deck 78 and comprisesa twin sheet structure including a lower sheet 94 coacting with an uppersheet 96 to define the main body intermeshing boss panel structure ofthe deck with enlarged upwardly and downwardly extending bosses 94a and96a provided in the leg or column regions of the pallet in the patternshown in FIG. 19 so that, as with the upper deck 78, each leg or columnsection of the lower deck defines a rectangular wall or column with alinear column positioned within the rectangular column and with openings98 in the downwardly extending bosses forming the inner walls of therectangular column opening into the interior of the respective boss inthe manner described with respect to the openings 92. The completedpallet defines a load receiving surface 100 at the upper face of theupper deck and defines a flat lower surface 102 at the lower face of thelower deck to support the pallet.

The invention will be seen to provide a panel structure that islightweight, strong, durable and maintenance-free, provides all-weatherperformance, and is relatively inexpensive. The invention panelstructure is thereby ideally suited for a myriad of construction andfabricating applications.

More specifically, pallets constructed in accordance with the inventionhave been found to have superior structural strength as compared toprior art twin sheet pallets and even as compared to applicant'simproved prior art twin sheet pallet shown in U.S. Pat. No. 4,879,956.Specifically, as compared to prior art twin sheet pallets, the inventiondesign enables the invention pallet to be constructed utilizingsignificantly less plastic material than the prior art twin sheetdesigns while providing the same structural strength. Since the plasticmaterial constitutes a significant part of the cost of a twin sheetpallet, a significant reduction in the amount of material required tomeet any particular structural requirement enables the entire pallet tobe manufactured at a cost significantly less than pallets of thedescribed prior art twin sheet design.

Whereas the particular plastic material utilized to form the inventionpallet is not critical, it has been found that excellent results may beobtained by the use of a high density polyethylene having a density ofapproximately 0.950 grams per cubic centimeter.

Whereas preferred embodiments of the invention have been illustrated anddescribed in detail, it will be apparent that various changes may bemade in the disclosed embodiments without departing from the scope orspirit of the invention. For example, although the bosses have beenillustrated and described as having a circular cross-sectionalconfiguration, other cross sectional configurations such as, but notlimited to, rectangular or oval configurations, may be employed and theterm annular as used in the claims to describe, the side walls of thebosses will be understood to include any closed loop cross-sectionalconfiguration.

I claim:
 1. A twin sheet panel structure comprising an upper plasticsheet including a planar main body portion having upper and lowersurfaces and a lower plastic sheet positioned in parallel spacedrelation below said upper plastic sheet and including a main bodyportion having upper and lower surfaces, the upper sheet furtherincluding a plurality of spaced hollow bosses opening in the uppersurface of the upper sheet main body portion and each including anannular side wall portion extending downwardly from the lower surface ofsaid upper sheet main body portion and a lower wall portion at a lowerend of the side wall portion, the lower plastic sheet further includinga plurality of spaced hollow bosses opening in the lower surface of thelower sheet main body portion and each including an annular side wallportion extending upwardly from the upper surface of the lower sheetmain body portion and an upper wall portion at an upper end of the sidewall portion, characterized in that:the annular side wall portions havea generally circular cross-sectional configuration; the combined area ofthe openings of the downwardly extending bosses of the upper sheet inthe upper surface of the upper sheet main body portion constitutes lessthan half of the total surface area of the upper surface of the mainbody portion of the upper sheet; the combined area of the openings ofthe upwardly extending bosses of the lower sheet in the lower surface ofthe lower sheet main body portion constitutes less than half of thetotal surface area of the lower surface of the main body portion of thelower sheet; and the annular side wall portions of some of said uppersheet bosses are fused to the annular side wall portions of some of saidlower sheet bosses.
 2. A panel structure according to claim 1 whereinthe lower wall portions of the upper sheet bosses are positioned incontiguous spaced relation on the upper surface of the main body portionof the lower sheet and the upper wall portions of the lower sheet bossesare positioned in contiguous spaced relation on the lower surface of themain body portion of the upper sheet.
 3. A panel structure according toclaim 2 wherein the lower wall portions of the upper sheet bosses arefused to the upper surface of the main body portion of the lower sheetand the upper wall portions of the lower sheet bosses are fused to thelower surface of the main body portion of the upper sheet.
 4. A panelstructure according to claim 1 wherein at least some of said downwardlyextending bosses on said upper sheet are positioned in spaces betweenadjacent upwardly extending bosses on said lower sheet.
 5. A panelstructure according to claim 1 wherein the upper sheet bosses arearranged in a defined grouping with the bosses in the grouping spacedfrom each other, the lower sheet bosses are arranged in a definedgrouping complementary to the upper sheet grouping with the bosses inthe lower sheet grouping spaced from each other, and the bosses in theupper sheet grouping fit in complementary fashion into spaces betweenthe bosses in the lower sheet grouping with the side wall portions ofthe upper sheet bosses fused to the side wall portions of the lowersheet bosses.
 6. A panel structure according to claim 1 wherein thefused together upper sheet bosses and lower sheet bosses are arranged inparallel rows with each row including alternate upper sheet bosses andlower sheet bosses.
 7. A panel structure according to claim 1 whereinthe annular side wall portions of said first and second sheet bossestaper inwardly in complementary fashion so as to define angledinterfaces therebetween and said side wall portions are fused togetherat their angled interfaces.
 8. A twin sheet panel structure comprisingan upper plastic sheet including a planar main body portion having upperand lower surfaces and a plurality of spaced hollow bosses opening inthe upper surface of the main body portion and each including an annularside wall portion extending downwardly from the lower surface of themain body portion and a lower wall portion at lower end of the side wallportion, and a lower plastic sheet including a planar main body portionhaving a lower surface, and an upper surface fused to the lower wallportions of said upper sheet bosses, and a plurality of spaced hollowbosses opening in the lower surface of the lower sheet main body portionand each including an annular side wall portion extending upwardly fromthe upper surface of the lower sheet main body portion and an upper wallportion at an upper end of the side wall portion, said upper wallportions of said lower sheet bosses being fused in spaced relation tothe lower surface of said upper sheet main body portion, characterizedin that:the annular side wall portions have a generally circularcross-sectional configuration; the combined area of the openings of thedownwardly extending bosses of the upper sheet in the upper surface ofthe upper sheet main body portion constitutes less than half of thetotal surface area of the upper surface of the main body portion of theupper sheet; the combined area of the opening of the upwardly extendingbosses of the lower sheet in the lower surface of the lower sheet mainbody portion constitutes less than half of the total surface area of thesurface of the main body portion of the lower sheet; and side wallportions of upper sheet bosses are arranged in contiguous relation toside wall portions of lower sheet bosses with the contiguous side wallportions fused together.
 9. A panel structure according to claim 8wherein the annular side wall portions of said upper and lower sheetbosses taper inwardly in complementary fashion so as to define angledinterfaces therebetween and said side wall portions are fused togetherat their angled interfaces.
 10. A twin sheet panel structure comprisinga first plastic sheet including a planar main body portion having innerand outer surfaces and a second plastic sheet positioned in parallelspaced relation to said first plastic sheet and including a main bodyportion having an outer surface and an inner surface confronting theinner surface of the main body portion of said first sheet,characterized in that the first plastic sheet further includes aplurality of generally parallel laterally extending rows of hollowbosses opening in the outer surface of the first sheet main body portionwith the bosses in each row laterally spaced from each other and witheach boss including an annular side wall portion extending inwardly fromthe inner surface of the first sheet and an inner wall portion at theinner end of the side wall portion, the second plastic sheet furtherincludes a plurality of generally parallel laterally extending rows ofhollow bosses opening in the outer surface of the second sheet main bodyportion with the bosses in each row laterally spaced from each other andwith each boss including an annular side wall portion extending inwardlyfrom the inner surface of the second sheet and an inner wall portion atthe inner end of the side wall portion, the annular side wall portionshave a generally circular cross-sectional configuration, the combinedarea of the openings of the inwardly extending bosses of the first sheetin the outer surface of the main body portion of the first sheetconstitutes less than half of the total surface area of the outersurface of the main body portion of the first sheet, the combined areaof the openings of the inwardly extending bosses of the second sheet inthe outer surface of the second sheet main body portion constitutes lessthan half of the total surface area of the outer surface of the mainbody portion of the second sheet, and the bosses in a row of said firstsheet are interdigitated with the bosses in a corresponding row of thesecond sheet with the adjacent side wall portions of the interdigitatedbosses fused together to form a plurality of rigid column structuresbetween the sheets corresponding to said rows.
 11. A panel structureaccording to claim 10 wherein the inner wall portion of each boss ofsaid first sheet is fused to the inner surface of the main body portionof said second sheet and the inner wall portion of each boss of saidsecond sheet is fused to the inner surface of the main body portion ofsaid first sheet.
 12. A twin sheet plastic pallet comprising an upperplastic sheet including a planar main body portion having an uppersurface defining a load receiving surface and a lower plastic sheetpositioned in downwardly spaced relation below the upper plastic sheetand including a main body portion having a lower surface, the uppersheet further including a plurality of spaced hollow bosses opening inthe upper surface of the upper sheet main body portion and eachincluding an annular side wall portion extending downwardly from saidupper sheet main body portion and a bottom wall portion at the lower endof said side wall portion fused to the upper surface of the main bodyportion of said lower sheet, and the lower plastic sheet furtherincluding a plurality of spaced hollow bosses opening in the lowersurface of the lower sheet main body portion and each including anannular side wall portion extending upwardly from said lower sheet mainbody portion and a top wall portion at the upper end of said side wallportion fused to the lower surface of said upper sheet main bodyportion, characterized in that:the annular side wall portions have agenerally circular cross-sectional configuration, the annular side wallportions of some of the upwardly extending bosses are fused to theannular side wall portions of some of the downwardly extending bosses,the combined area of the openings of the downwardly extending bosses ofthe upper sheet in the upper surface of the upper sheet main bodyportion constitutes less than half of the total surface area of theupper surface of the main body portion of the upper sheet, and thecombined area of the openings of the upwardly extending bosses of thelower sheet in the lower surface of the lower sheet main body portionconstitutes less than half of the total surface area of the lowersurface of the main body portion of the lower sheet.
 13. A palletaccording to claim 12 wherein at least some of the upwardly extendingbosses are positioned in spaces between adjacent downwardly extendingbosses.
 14. A pallet according to claim 12 wherein the fused togetherupwardly extending bosses and downwardly extending bosses are arrangedin parallel rows.
 15. A pallet according to claim 12 wherein the annularside wall portions of said upper and lower sheet bosses taper inwardlyin complementary fashion so as to define angled interfaces therebetweenand said side wall portions are fused together at their angledinterfaces.
 16. A pallet according to claim 12 wherein said fusedtogether upper and lower sheets coact to define a platform structure ofsaid pallet and said pallet further includes a plurality of spaced legsextending downwardly from said platform structure.
 17. A twin sheetplastic pallet including an upper plastic sheet including a planar mainbody portion having upper and lower surfaces and a lower plastic sheetpositioned in downwardly spaced relation below the upper plastic sheetand including a main body portion having upper and lower surfaces,characterized in that the upper plastic sheet further includes aplurality of hollow bosses opening in the upper surface of the firstsheet main body portion with the bosses arranged in a defined groupingof spaced bosses and with each boss including an annular side wallportion extending downwardly from the lower face of the upper sheet mainbody portion and a bottom wall portion at the lower end of the side wallportion, the lower plastic sheet further includes a plurality of hollowbosses opening in the lower surface of the second sheet main bodyportion with the bosses arranged in a defined grouping complementary tothe defined grouping of the upper sheet bosses and with each bossincluding an annular side wall portion extending upwardly from the uppersurface of the main body portion of the lower sheet and a top wallportion at the upper end of the side wall portion, the annular side wallportions have a generally circular cross-sectional configuration, thebosses in the defined grouping of upper sheet bosses are interdigitatedwith respect to the complementary defined grouping of lower sheet bosseswith the adjacent side wall portions of the interdigitated bosses fusedtogether to form a rigid structure between the upper and lower sheetscorresponding to the interdigitated defined groupings, the combined areaof the openings of the downwardly extending bosses of the upper sheet inthe upper surface of the upper sheet main body portion constitutes lessthan half of the total surface area of the upper surface of the mainbody portion of the upper sheet, and the combined area of the openingsof the upwardly extending bosses of the lower sheet in the lower surfaceof the lower sheet main body portion constitutes less than half of thetotal surface area of the lower surface of the main body portion of thelower sheet.
 18. A pallet according to claim 17 wherein the bottom wallof each boss of said upper sheet is fused to the upper surface of themain body portion of said lower sheet and the top wall of each boss ofsaid lower sheet is fused to the lower surface of the main body portionof said upper sheet.
 19. A pallet according to claim 17 wherein thefused together upper and lower sheets coact to define a platformstructure of said pallet and said pallet further includes a plurality ofspaced legs extending downwardly from said platform structure.
 20. Apallet according to claim 19 wherein said pallet further includes a basestructure secured to the lower ends of said legs so that said legs, saidplatform structure, and said base structure coact to define passagewaysfor the receipt of material handling equipment.
 21. A pallet accordingto claim 20 wherein said base structure has a construction correspondingto the construction of said platform structure and including upper andlower sheets respectively defining downwardly extending and upwardlyextending interdigitated bosses with the side walls of at least some ofthe upwardly extending bosses fused to the side walls of some of thedownwardly extending bosses.
 22. A pallet according to claim 21 whereinsaid legs are formed of panel structures having upper and lower sheetsrespectively defining upwardly and downwardly extending hollow bossesarranged in interdigitated fashion with annular side wall portions ofsome of the upwardly extending bosses fused to annular side wallportions of some of the downwardly extending bosses.
 23. A palletaccording to claim 21 wherein some of the upwardly and downwardlyextending bosses of the upper and lower sheets respectively of theplatform structure are larger than the remaining upwardly and downwardlyextending bosses of the platform structure and these larger bosses areintermeshingly fused together to form leg structures.
 24. A palletaccording to claim 23 wherein some of the upwardly and downwardlyextending bosses of the upper and lower sheets respectively of the basestructure are larger than the remaining upwardly and downwardlyextending bosses of the base structure, these larger bosses areintermeshingly fused together to form leg structures, and the platformstructure leg structures are fused to the base structure leg structuresto form the legs.
 25. A pallet according to claim 17 wherein the annularside wall portions of said upper and lower sheet bosses taper inwardlyin complementary fashion so as to define angled interfaces therebetweenand said side wall portions are fused together at their angledinterfaces.